US20070130951A1

US20070130951A1 - Combustor

Info

Publication number: US20070130951A1
Application number: US11/377,685
Authority: US
Inventors: Hae Choi; Hyung Park; Woo Jeon
Original assignee: Seoul National University Industry Foundation
Current assignee: Seoul National University Industry Foundation
Priority date: 2005-12-10
Filing date: 2006-03-17
Publication date: 2007-06-14
Also published as: KR100715027B1

Abstract

Provided is a combustor comprising an entrance through which the fuel flows thereinto; a combustion chamber, connected to the entrance, having a larger cross-section area than that of the entrance; and a plurality of protrusions installed along the interface of the entrance and the combustion chamber. Thus, the combustor according to the present invention has an enhanced mixing capability of fuel and air in the combustion chamber, thereby having enhanced combustion efficiency and reduced discharge of harmful exhaust gas.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2005-0121254, filed on Dec. 10, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a combustor, and more particularly, a combustor having an improved structure that increases the combustion efficiency and reduces the discharge of harmful exhaust gas by enhancing the mixing of fuel and air in a combustion chamber.
2. Description of the Related Art
A power generator such as a gas turbine or jet engine generates power by combusting a mixture of hydrocarbon fuel, e.g., natural gas and air.
To mix fully the fuel and air is essential in increasing the efficiency of the combustor. Thus, the enhancement of the mixing capability of the combustion chamber is very important in increasing the efficiency of the combustor.
When the fuel and air are mixed poorly, imperfect combustion is caused. Thus, the efficiency of the combustor decreases and the discharge of harmful exhaust gas after combustion causes the air pollution.
As shown in FIG. 1, a conventional combustor 1 includes an entrance 2 through which the fuel flows into the combustion chamber 3. The combustion chamber 3 has a larger cross-section area than that of the entrance 2. The fuel flowing through the entrance 2 is mixed with the air in the combustion chamber 3 for combustion.
Thus, the whole flow in the entrance and the combustion chamber 3 can be approximated to the flow over a backward-facing step having sudden expansion as shown in FIG. 2. Referring to FIG. 2, the incoming flow separates at the trailing edge of the step 6, reattaches and redevelops at the downstream wall, some distance apart from the step 6. The location where the separated flow reattaches is called reattachment region 5 and the distance between the step 6 and the reattachment region 5 is denoted by reattachment length (L). On the other hand, there exists a strong vortical motion behind a step 6 creating so-called recirculation region 4. Due to this vortical motion, the flow in the recirculation region 4 is not mixed well with the surrounding outer flow.
Because of the similarities between the backward-facing step flow and the fuel flow into the combustion chamber, there also exists the recirculation region in the combustion chamber. Hence, this causes the poor mixing in the combustion chamber and eventually the lower efficiency of the combustor with discharge of harmful gases as explained above.

SUMMARY OF THE INVENTION

The present invention provides a combustor, in which power is generated by combusting the mixture of fuel and air, having an improved structure that increases the efficiency and reduces the discharge of harmful gas by enhancing the mixing of the fuel and air in the combustion chamber.
According to the aspect of the present invention, there is provided a combustor comprising an entrance through which the fuel flows there into; a combustion chamber, connected to the entrance and having a larger cross-section area than that of the entrance; and a plurality of protrusions installed along the interface between the entrance and the combustion chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The overall features and advantages of the present invention will become more apparent by describing an exemplary embodiment in detail thereof with reference to the attached drawings in which:
FIG. 1 is a sectional view of a conventional combustor.
FIG. 2 is a view for typical backward-facing step flow having flow separation, reattachment and recirculation region as those in the combustor in FIG. 1.
FIG. 3 is a sectional view of a combustor (entrance of a combustion chamber) according to an exemplary embodiment of the present invention.
FIG. 4 is a sectional view taken along the IV-IV line of the combustor in FIG. 3.
FIG. 5 is a schematic view of an experimental setup to prove the effects of the combustor according to an exemplary embodiment of the present invention.
FIG. 6 is a graph showing the results of the experiments illustrated in FIG. 5.
FIG. 7 is a sectional view of a combustor according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described in more detail with reference to the drawings accompanied, in which preferred embodiments of the present invention are illustrated.
FIG. 3 is a sectional view of a combustor according to an embodiment of the present invention, and FIG. 4 is a IV-IV sectional view of the combustor in FIG. 3.
Referring to FIGS. 3 and 4, a combustor of present exemplary embodiment comprises an entrance 10, a combustion chamber 20 and a plurality of protrusions 30.
The entrance 10 has a circular cross-section and fuel flows into the combustion chamber 20 through the entrance 10. In general, gaseous fuel flows through the entrance 10. However liquid fuel can also flow through the entrance 10, and in this case, the liquid fuel is sprayed into the entrance 10 through a nozzle.
The combustion chamber 20 is connected to the entrance 10 and is formed so as to have a larger cross-section area than that of the entrance 10. The combustion chamber 20 has a circular cross-section, also. The fuel flowing through the entrance 10 is mixed with the air in the combustion chamber 20.
The protrusions 30 are installed at the interface between the entrance 10 and the combustion chamber 20 with same spacing between adjacent protrusions. The protrusion 30 is used as a device for reducing reattachment length, distance between the interface of the entrance 10 and the combustion chamber 20 and the reattachment region of the separated flow, which indicates the mixing enhancement in the combustion chamber.
Each protrusion 30 has a rectangular shape as show in FIGS. 3 and 4, and the vertical height (a) of the protrusion 30 should be 0.1 to 0.3 times the radius difference (d) between the radius of the cross-section of the entrance 10 and the radius of the cross-section of the combustion chamber 20. When the vertical height (a) is less than 0.1 d, it is difficult to obtain any effect of mixing enhancement. Also, when the vertical height (a) is larger than 0.3 d, the effect of mixing enhancement of fuel and air is not better compared to the cases where the vertical height (a) is about 0.1 d˜0.3 d.
Additionally the width (b) of the protrusion 30 should be 0.2 to 0.5 times the radius difference (d). When the width (b) is less than 0.2 d, it is difficult to obtain any effect of mixing enhancement. Also, when the width (b) is larger than 0.5 d, the effect of mixing enhancement of fuel and air is not better compared to the cases where the width (b) is about 0.2 d˜0.5 d.
Further, the spacing between the adjacent protrusions 30 should be 1.5 to 3.0 times the radius difference (d). When the spacing is less than 1.5 d, the mixing capabilities of the fuel and air become rather poor. When the spacing is larger than 3.0 d, the effect of mixing enhancement of fuel and air is not better compared to the cases where the spacing is about 1.5 d˜3.0 d.
The angle (θ) between a protruding direction of the protrusion 30 and a flow direction of the fuel at the interface between the entrance 10 and the combustion chamber 20 should be from 45° to 90°. When the angle (θ) is less than 45°, the mixing efficiency of the fuel and air decreases because the strength of the vortex in the flow direction generated by the protrusions 30 is reduced. When the angle (θ) is larger than 90°, the mixing efficiency of the fuel and air also decreases due to the same reason.
The combustor 100 described as above according to the embodiment of the present invention has the following functions.
Since the velocities of the fuel flow through the entrance 10 vary along the streamwise and radial directions only due to its circular cross-section, the flow can be approximated as a two-dimensional (axisymmetric) flow. When the fuel flow having nominally two-dimensional characteristics faces the protrusions 30, the streamwise vortices are generated at the edges of the protrusions 30. Due to this flow-modification by the protrusions 30, the velocity-fields change along the circumferential direction of the cross-section and thus the flow changes into the three-dimensional state.
For the aforementioned reasons, the flow in the combustion chamber 20 changes from two-dimensional to three-dimensional state by the protrusions 30. This three-dimensionality of the flow induces a more vigorous interaction of the fuel and air and subsequently reduces the size of the recirculation region, i.e. the reattachment length.
The capability of the mixing enhancement of the fuel and air in the combustion chamber 20 according to the embodiment of the present invention can be also confirmed by the following wind tunnel experiment.
The fuel flow to the combustion chamber 20 through an entrance 10 can be approximated to a flow over a backward-facing step with the protrusions 30 installed at the trailing edge of the step, as shown in FIG. 5.
Generally the Reynolds number of the flow inside the combustor 100 is in the range of 10,000 to 1,000,000. However the characteristics of the flow over a backward-facing step do not changes greatly with respect to the Reynolds number, if the flow is fully-developed turbulent state before separation. Thus, the effect of the protrusions 30 according to the embodiment of the present invention can be surely confirmed by the following experiment:
In the experimental setup, the height (h) of the step corresponds to the radius difference (d) in the embodiment of the present invention. The height (h) of the step is 30 mm and the protrusions 30 are installed at the trailing edge of the step with spacing of 2.33 h between adjacent protrusions. The protrusions 30 have the rectangular shape with a vertical height (a) of 0.3 h and a width (b) of 0.3 h. The incoming velocity is 12 m/s with a fully-developed turbulent boundary layer at the trailing edge of the step. Reynolds number is 24,000 based on the step height (h) and the incoming velocity of the flow.
FIG. 6 shows the results of the experiment conducted under the above conditions. In FIG. 6, the variations of the reattachment length (x_R) with and without the protrusions are plotted together. The solid and dotted lines denote the reattachment length (x_R) normalized by the step height (h) for the cases without and with protrusions, respectively. The horizontal and vertical axes denote the spanwise distance from the center of the step, normalized by the step height (h) (here z_cdenotes the protrusion center) and the reattachment length (x_R) normalized by the step height (h), respectively. From FIG. 6, we can clearly see that the reattachment length (x_R) with protrusions reduces about 40% in average (80% in local maximum) compared to the case without protrusions.
When the reattachment length (x_R) of the flow decreases, the mixing between the fuel and air is enhanced, thereby increasing the combustion efficiency of the fuel and ultimately improving the combustion capacity of the combustor 100. In addition, when the well-mixed mixture of fuel and air is combusted, a quantity of exhaust gas generated by the imperfect combustion of the fuel remarkably decreases, thereby preventing the environmental pollution.
The combustor 100 is not limited to the structure described above and illustrated in the drawings.
For example, the entrance 10 and the combustion chamber 20 are described as having a circular cross-section, but they may have an oval or polygonal cross-section also.
The vertical height (a) of the protrusion 30 is described as being 0.1 d to 0.3 d, the width (b) of the protrusion 30 as being 0.2 d to 0.5 d, and the spacing between the adjacent protrusions 30 as being 1.5 d to 3.0 d. However, protrusions of the combustor may have other configurations also.
The protrusions 30 are described as having a rectangular shape, but they may have any shape as long as they protrude on the interface between the entrance 10 and the combustion chamber 20. For example, the protrusion may have a triangular shape also.
The combustion chamber 20 is described as having a constant cross-section, but may have a cross-section increasing or decreasing along the flow direction.
FIG. 7 shows a combustor 200 according to another embodiment of the present invention. The combustor 200 has the same entrance 10 and protrusions 30 as the combustor 100 in FIG. 3. A combustion chamber 40 includes a slanted portion 41 and an extended portion 42. The slanted portion 41 is connected to an end of the entrance 10 in the flow direction. In the slanted portion 41, the cross-section increases along the flow direction. The extended portion 42 is connected to an end of the slanted portion 41 in the flow direction. In the extended portion 42, the cross-section is constant along the streamwise direction. In the combustor 200, the fuel flowing into the combustion chamber becomes a three-dimensional flow due to the protrusions 30, and as a result, the combustor 200 has a short reattachment length that enhances the mixing of the fuel and air.
As described above, the combustor according to the embodiments of the present invention has an improved structure to enhance the mixing of the fuel and air flowing thereinto. Thus, the combustion efficiency of the combustor is improved and the discharge of the harmful exhaust gas is reduced.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

Claims

1. A combustor comprising:

an entrance through which the fuel flows into the combustion chamber;

a combustion chamber, connected to the entrance having a larger cross-section area than that of the entrance; and

a plurality of protrusions installed along the interface between the entrance and the combustion chamber.

2. The combustor of claim 1, wherein each protrusion forms an angle between 45° to 90° with respect to a flow direction of the fuel at the entrance.

3. The combustor of claim 2, wherein the cross-sections of the entrance and the combustion chamber are circular and the protrusions are installed with a same spacing between adjacent protrusions.

4. The combustor of claim 3, wherein the combustion chamber includes a slanted portion, connected to the entrance having a cross-section increasing from the entrance toward the flow direction of the fuel and air; and an extended portion, connected to the slanted portion having a constant cross-section;

the height of the protrusion is 0.1 to 0.3 times the difference between the radius of the cross-section of the entrance and the radius of the cross-section of the extension portion;

the width of the protrusion is 0.2 to 0.5 times the difference between the radius of the cross-section of the entrance and the radius of the cross-section of the extension portion; and

the spacing between the protrusions is 1.5 to 3 times the difference between the radius of the cross-section of the entrance and the radius of the cross-section of the extension portion.

5. The combustor of claim 1, wherein each protrusion has a rectangular shape

6. The combustor of claim 1, wherein each protrusion has a triangular shape.